Siobhan McLaughlin, 46, was refused the benefit after her partner John Adams died from cancer in January 2014 because the couple, who had four children and were together for 23 years, were not married or in a civil partnership.

She initially won a case after claiming unlawful discrimination based on her marital status, but that ruling was later overturned by the Court of Appeal.

However, by a majority of four justices to one, the Supreme Court ruled this morning that the current law on the allowance is ‘incompatible’ with Human Rights legislation.

Giving the lead judgement, the court’s President Lady Hale said: ‘The allowance exists because of the responsibilities of the deceased and the survivor towards their children.

‘Those responsibilities are the same whether or not they are married to or in a civil partnership with one another.

‘The purpose of the allowance is to diminish the financial loss caused to families with children by the death of a parent.

‘That loss is the same whether or not the parents are married or in a civil partnership with one another.’

Ms McLaughlin was refused the benefit after her partner John Adams died from cancer in January 2014 because they were not married (PA)

However, Lady Hale said not every case where an unmarried parent is denied the allowance after the death of their partner will be unlawful.

The court also said it is up to the Government to decide whether or how to change the law.

Ms McLaughlin, a special needs classroom assistant from Armoy, Co Antrim, was with her partner John Adams, a groundsman, for 23 years and they had four children – Rebecca, 15, Billy, 16, Lisa, 21, and Stuart, 23.

Following Mr Adams’s death, Ms McLaughlin had to take on an evening job after being refused widowed parent’s allowance by the Northern Ireland Department for Communities.

‘Whilst the position of unmarried partners is still precarious, the rights afforded by this decision are certainly an improvement. It will allow people in the UK to apply for the widowed partner’s allowance….

‘Whilst it is a positive outcome, the vulnerable position of unmarried couples upon death has been highlighted.

‘They must ensure that wills are in place which clearly states the manner in which estates are to be divided so that proper provision is made for partners and children.’

A DWP spokesman said: We will consider the court’s ruling carefully.

‘Widowed parent’s allowance was a contributory benefit and it has always been the case that inheritable benefits derived from another person’s contributions should be based on the concept of legal marriage or civil partnership.

‘This ruling doesn’t change the current eligibility rules for receiving bereavement benefits, which are paid only to people who are married or in a civil partnership.’